Mr. Bowditch on the Longitude of Cambridge. 261 
_ The fifth observation is the total eclipse of the sun of June 16, 
1806. The time of conjunction deduced from my observations at 
Salem, compared with the time of conjunction at Paris, computed by 
La Lande, gives, by allowing 58 seconds for the difference of meridi- 
ans of Salem and Cambridge, the longitude of Cambridge 4A. 44 
24”-9 W from Greenwich, as is shown in the additional observations 
on that eclipse given in this memoir. 
The sixth observation is the transit of Venus of June 3, 1769.. 
The observations at Newbury and Cambridge make the conjunction 
at Cambridge at 5/, 20’ 18’"6, and those at Greenwich and Paris 
make the conjunction at Greenwich at 104. 4’ 49’*7 apparent time. 
The difference is the longitude of Cambridge by this observation 
Ah, 44' 31"*1, as will be shewn hereafter. 
Upon examination of the transactions of the Royal Societies of 
London and Paris, those of the Society held at Philadelphia and the 
Memoirs of the American Academy of Arts and Sciences, two more 
corresponding observations were found. The first was that of the 
transit of Mercury of Nov. 12, 1782, but this was very poorly adapt- 
ed to determine with accuracy the difference of meridians. . For the 
planet entered but 31 seconds on the sun’s disc, and the situation was 
such that a small error in the latitude of the planet would cause a great 
error in the difference of meridians, and it entered so obliquely on the 
sun’s limb that it was difficult to determine the precise moment of the 
contacts. This was particularly the case at Paris where the sun was 
low: the observers there differed above 4 minutes in the time of the 
first internal contact and above 2 minutes in the second external con- 
tact. In the transit of 1789, the planet was more favourably situated, 
as it respects its latitude, but the sun set before the end of the transit 
at Paris, and the weather prevented. making an observation of the be- 
ginning of the transit; the first internal contact was however obsery- 
33 
